Al-rich sludge produced from industrial anodising and surface treatment processes had
been tested in the fabrication of mullite-based materials, by using unidirectional dry pressing as
shaping technique. Mixture with common natural silica and magnesium-containing materials, like
ball clay, kaolin and diatomite were prepared in order to achieve interesting final fired refractory
and/or electrical insulating materials. Microstructural changes upon sintering and crystalline phase
evolution are detailed and their relationship with the electrical behaviour is also studied, by the use
of impedance spectroscopy. Finally, different models were used to fit the experimental electrical
resistivity values and to estimate the percolation limit of the bi-phase material.